If you really want to raise revenues, the Holy Grail isn't capping tax deductions, as Romney proposed, or raising the top marginal rate, as Obama proposed. It's taxing investment income like ordinary income.
Suddenly, Republicans are all about increasing tax revenues from rich people. In the last weeks of the campaign, Mitt Romney talked about capping itemized deductions for high-income taxpayers (which, unfortunately for his arithmetic, would not nearly have compensated for the lower tax rates he proposed). John Boehner has told his caucus that they have to be willing to accept increased tax revenues (but out of the other side of his mouth says that tax rates cannot be increased). Glenn Hubbard, in the Financial Times, also suggests increasing revenues by closing loopholes: "Tax deductions should be scaled back, especially in the areas of mortgage interest, charitable giving and employer-provided health insurance."
What do all of these proposals have in common? They pass silently over the most important loophole for the rich: artificially low tax rates on investment income, whether capital gains (profits from sales of assets) or dividends (cash distributions from corporations to shareholders).
Why won't a limit on deductions solve this problem? Because itemized deductions, like those for mortgage interest or charitable contributions, are only one type of tax loophole. Another is compensation that is not counted as income to begin with. It is "excluded," which is different from being "deducted" like employer-provided health benefits. And another is simply applying a lower tax rate to certain types of income. Since 2003, both long-term capital gains (sales of assets held for over one year) and most dividends have been taxed at a maximum rate of 15 percent, while the top rate on "ordinary" income (from, you know, working) has been 37.9 percent, if you include the Medicare payroll tax. This is why Mitt Romney, despite his hundreds of millions of dollars of wealth, pays a lower average tax rate than many middincome Americans.